The primary goal of this project is to determine how acoustic signals are represented, processed, and transmitted in cortex. Signal processing depends on several variables including: 1) the membrane properties of neurons; 2) the patterns of anatomical connections between the many types of neurons in cortex; and 3) the dynamic properties of synaptic transmission. An in vitro slice preparation of the mouse auditory cortex will be used to examine how these variables affect signal processing in a small network of neurons. Simultaneous whole-cell recordings from 2-5 interconnected neurons, each of which can be identified visually. The experiments of Aim 1 will determine the patterns of connections between the pyramidal neurons and the different types of excitatory and inhibitory neurons in cortex and characterize the properties of synaptic transmission between each neuron. The experiments of Aim 2 will determine which of these cells are innervated by thalamic afferents, a major source of input into the auditory cortex. At the completion of these two sets of experiments, the circuitry that process signals will be determined. The link between the input neurons (those that receive thalamic afferents) and the output neurons (pyramidal neurons) will be established. The experiments in Aim 3 will then examine, using a novel iterative procedure, how computergenerated signals delivered to the thalamus affects the firing of successive neurons in circuit. These experiments will provide both basic information about circuitry as well as provide insights as to how auditory signals are processed in cortex. This information may elucidate mechanisms of deafness as well as lead to better designs of cochlear implants.